1364160domain: NAppears in sequencesEach term is the previous term times the number of letters in the previous number, as conventionally spelled out in English.at n=6A129731a(n) = Sum_{0 < x,y,z,t <= n and gcd(x^2 + y^2 + z^2 + t^2, n)=1} gcd(x^2 + y^2 + z^2 + t^2 - 1, n).at n=28A239613